The present invention relates to a replaceable sleeve which may be readily mounted onto a cylindrical carrier, and more particularly, to a replaceable sleeve comprising a multilayer reinforced composite which may be cured in a single vulcanizing step.
Rubber-covered cylindrical rollers are widely used in industry for a number of applications, particularly for web or sheet handling and processing applications such as the embossing, calendering, laminating, printing and coating of paper, film, foil, and other materials. In addition to their use in web processing equipment, such rubber-covered rollers are often employed in conveyors and various office machines. Such rollers are typically comprised of a cylindrical (metal) core or other support with an outer covering of rubber, elastomer, or polymer material. However, after extended use, the covering on the rollers wears down and must be resurfaced or replaced. This typically requires that the rollers be sent to an outside source where the old surface is ground down and a new surface is applied. This is inconvenient and expensive as it requires that the processing equipment be shut down while the roller is being resurfaced or that the end user stock additional replacement rollers. Even in the latter instance, the rollers must be eventually sent out for resurfacing.
Cylindrical rollers are widely used in the printing industry. For example, printing rollers or sleeves are used in the flexographic printing industry for providing a mountable surface for flexographic printing plates. In a typical flexographic printing press, the sleeve is mounted onto a printing cylinder using pressurized air to expand the sleeve, and the printing plates are then attached to the outer surface of the sleeve.
While thin metal sleeves for use on printing cylinders have been employed in the past, more recently, printing sleeves have been developed which are comprised of polymeric materials. For example, printing sleeves are known which include laminated polymeric layers reinforced with a woven or nonwoven fabric layer. Such sleeves provide an advantage over metal rollers in that they are readily expandable for mounting on a cylinder, are seamless, and provide good structural integrity for printing operations without the damage and safety limitations of thin metal sleeves. However, such sleeves are typically expensive and slow to fabricate as each component must be formed and cured separately and then assembled or formed into a composite. Further, many polymeric printing sleeves in use require specific polymers and/or cure temperatures, which restricts the choice of materials or properties of the finished sleeve surface which may be desired for different printing applications.
Accordingly, there is still a need in the art for a replaceable sleeve which is readily mountable on a cylinder or other carrier, which may be fabricated quickly and easily, and which may be used in a wide variety of applications including printing applications as well as web or sheet handling or and/or processing applications and the like.
The present invention meets that need by providing a replaceable sleeve adapted to be mounted on a cylindrical carrier which is comprised of a multilayer composite and which may be used in a number of applications which typically utilize polymer covered rolls including but not limited to web or sheet handling operations and flexographic printing operations. The sleeve is efficiently produced as the layers comprising the sleeve may be cured simultaneously. The sleeve is essentially seamless, chemically resistant, and may be easily mounted on a variety of carriers. When used in printing operations, the sleeve provides high print quality and performs within the tolerance levels required by the printing industry.
According to one aspect of the present invention, a replaceable sleeve is provided which is adapted to be mounted on a carrier. By carrier, we mean any structure which functions to support the sleeve during use and allows it to rotate during use including but not limited to cylinders, tubes, and liners. The replaceable sleeve is made up of a combination of layers including an inner polymeric layer, a reinforcing layer overlying the inner layer, an intermediate polymeric layer overlying the reinforcing layer, and an outer polymeric layer forming a working surface, where the Shore A hardness of the inner polymeric layer is generally equal to or greater than the Shore A hardness of the intermediate and outer polymeric layers. By working surface, we mean that the outer surface of the sleeve may be adapted for a number of uses such as printing, embossing, coating, calendering, etc.
Preferably, the inner layer, intermediate layer, and outer layer are comprised of an elastomeric material selected from, but not limited to, the group consisting of butyl rubber, nitrile rubber, EPDM rubber, natural rubber, synthetic rubber, neoprene rubber, a blend of nitrile rubber and polyvinyl chloride, and polyurethane. Further, the inner layer, intermediate layer, and outer layer preferably have a Shore A durometer hardness of from about 30 to 90.
In a preferred embodiment, the inner layer has a Shore A hardness of at least about 70, and comprises, for example, a carboxylated nitrile-butadiene copolymer. The inner layer enhances the durability of the sleeve for repeated usage.
The reinforcing layer is preferably comprised of wound fibers of a material selected from the group consisting of polyester, cotton, fiberglass, cotton-wrapped polyester, rayon, carbon filaments, and other high modulus synthetic or organic fibers.
In a preferred embodiment of the invention, the sleeve further includes a cushion layer which may be positioned between the intermediate polymeric layer and the outer surface layer which functions to provide energy absorption and resiliency to the sleeve. The cushion layer may be comprised of an open or closed-cell polymeric foam or a polymer layer having a Shore A durometer hardness of from about 25 to 55.
The outer polymeric layer functions both as a protective layer for the cushion layer as well as providing a working surface having the particular characteristics needed for a specific end use. Preferably, each of the layers comprising the sleeve has a thickness of from about 0.001 to 0.750 inches (0.0025 cm to 1.905 cm).
The present invention also provides a method of making the replaceable sleeve of the present invention, which comprises the steps of forming an inner layer of a hard polymeric material into a cylindrical shape and mounting the layer on a support. A reinforcing layer is applied over the outer surface of the inner layer, and an intermediate polymeric layer is applied over the outer surface of the reinforcing layer. An outer polymeric layer may be applied over the outer surface of the intermediate polymeric layer. The layers are then cured simultaneously in a single step to form the sleeve. The layers are preferably cured at a temperature of between about 285xc2x0 F. to 310xc2x0 F. (140xc2x0 C. to 154xc2x0 C.) and for a time to effect vulcanization of all of the layers.
The method also includes the optional step of applying a cushion layer over the outer surface of the intermediate polymeric layer prior to applying the outer layer. Where the cushion layer is comprised of an open or closed-cell polymeric foam, the cellular structure may be formed in a separate step prior to aplying the outer layer.
The outer surface of the resulting sleeve may be further processed as desired to provide a working surface for specific applications. For example, the outer layer may be ground to provide a surface roughness which is suitable for applications such as coating, calendering, laminating, and the like, or which may be polished, etched or engraved to provide a surface which may be used for embossing or printing. The sleeve may be readily mounted and dismounted from a carrier using pressurized air. In addition to the printing and coating applications described above, the sleeve may be used in any other applications which require the use of a polymer covered roller, such as flood/solid color print rolls, meter rolls, nip rolls, support rolls, and the like.
Accordingly, it is a feature of the present invention to provide a replaceable sleeve having a working surface which may be readily mounted on a carrier, which is easily fabricated, and which may be used in a variety of applications. This, and other features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.